Re: [PATCH v2 4/7] ghes_edac: avoid multiple calls to dmi_walk()

Steven Rostedt
2017-08-16T13:59:01Z

On Wed, 16 Aug 2017 10:29:31 +0200
Borislav Petkov <bp@alien8.de> wrote:

> ---
> diff --git a/drivers/edac/ghes_edac.c b/drivers/edac/ghes_edac.c
> index 6f80eb65c26c..a22fabef4791 100644
> --- a/drivers/edac/ghes_edac.c
> +++ b/drivers/edac/ghes_edac.c
> @@ -28,10 +28,14 @@ struct ghes_edac_pvt {
> char msg[80];
> };
>
> -static LIST_HEAD(ghes_reglist);
> -static DEFINE_MUTEX(ghes_edac_lock);
> -static int ghes_edac_mc_num;
> +static struct ghes_edac_pvt *ghes_pvt;
>
> +/*
> + * Sync with other, potentially concurrent callers of
> + * ghes_edac_report_mem_error(). We don't know what the
> + * "inventive" firmware would do.
> + */
> +static DEFINE_SPINLOCK(ghes_lock);
>
> /* Memory Device - Type 17 of SMBIOS spec */
> struct memdev_dmi_entry {
> @@ -169,14 +173,11 @@ void ghes_edac_report_mem_error(struct ghes *ghes, int sev,
> enum hw_event_mc_err_type type;
> struct edac_raw_error_desc *e;
> struct mem_ctl_info *mci;
> - struct ghes_edac_pvt *pvt = NULL;
> + struct ghes_edac_pvt *pvt = ghes_pvt;
> + unsigned long flags;
> char *p;
> u8 grain_bits;
>
> - list_for_each_entry(pvt, &ghes_reglist, list) {
> - if (ghes == pvt->ghes)
> - break;
> - }
> if (!pvt) {
> pr_err("Internal error: Can't find EDAC structure\n");
> return;
> @@ -398,8 +399,16 @@ void ghes_edac_report_mem_error(struct ghes *ghes, int sev,
> (e->page_frame_number << PAGE_SHIFT) | e->offset_in_page,
> grain_bits, e->syndrome, pvt->detail_location);
>
> - /* Report the error via EDAC API */
> + /*
> + * We can do the locking below because GHES defers error processing
> + * from NMI to IRQ context. Whenever that changes, we'd at least
> + * know.
> + */
> + WARN_ON_ONCE(in_nmi());

Should the above be:

if (WARN_ON_ONCE(in_nmi()))
return;

To prevent a deadlock? Or do we not care?

> +
> + spin_lock_irqsave(&ghes_lock, flags);
> edac_raw_mc_handle_error(type, mci, e);
> + spin_unlock_irqrestore(&ghes_lock, flags);

The above looks fine, as long as there's nothing before it that needs
synchronization.

> }
> EXPORT_SYMBOL_GPL(ghes_edac_report_mem_error);
>
> @@ -409,9 +418,14 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev)
> int rc, num_dimm = 0;
> struct mem_ctl_info *mci;
> struct edac_mc_layer layers[1];
> - struct ghes_edac_pvt *pvt;
> struct ghes_edac_dimm_fill dimm_fill;
>
> + /*
> + * We have only one logical memory controller to which all DIMMs belong.
> + */
> + if (ghes_pvt)
> + return 0;

What's the likelihood of two calls to ghes_edac_register being done
simultaneously? Because two calls at the same time will get past this.

-- Steve

> +
> /* Get the number of DIMMs */
> dmi_walk(ghes_edac_count_dimms, &num_dimm);
>
> @@ -425,26 +439,17 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev)
> layers[0].size = num_dimm;
> layers[0].is_virt_csrow = true;
>
> - /*
> - * We need to serialize edac_mc_alloc() and edac_mc_add_mc(),
> - * to avoid duplicated memory controller numbers
> - */
> - mutex_lock(&ghes_edac_lock);
> - mci = edac_mc_alloc(ghes_edac_mc_num, ARRAY_SIZE(layers), layers,
> - sizeof(*pvt));
> + mci = edac_mc_alloc(1, ARRAY_SIZE(layers), layers, sizeof(struct ghes_edac_pvt));
> if (!mci) {
> pr_info("Can't allocate memory for EDAC data\n");
> - mutex_unlock(&ghes_edac_lock);
> return -ENOMEM;
> }
>
> - pvt = mci->pvt_info;
> - memset(pvt, 0, sizeof(*pvt));
> - list_add_tail(&pvt->list, &ghes_reglist);
> - pvt->ghes = ghes;
> - pvt->mci = mci;
> - mci->pdev = dev;
> + ghes_pvt = mci->pvt_info;
> + ghes_pvt->ghes = ghes;
> + ghes_pvt->mci = mci;
>
> + mci->pdev = dev;
> mci->mtype_cap = MEM_FLAG_EMPTY;
> mci->edac_ctl_cap = EDAC_FLAG_NONE;
> mci->edac_cap = EDAC_FLAG_NONE;
> @@ -452,36 +457,23 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev)
> mci->ctl_name = "ghes_edac";
> mci->dev_name = "ghes";
>
> - if (!ghes_edac_mc_num) {
> - if (!fake) {
> - pr_info("This EDAC driver relies on BIOS to enumerate memory and get error reports.\n");
> - pr_info("Unfortunately, not all BIOSes reflect the memory layout correctly.\n");
> - pr_info("So, the end result of using this driver varies from vendor to vendor.\n");
> - pr_info("If you find incorrect reports, please contact your hardware vendor\n");
> - pr_info("to correct its BIOS.\n");
> - pr_info("This system has %d DIMM sockets.\n",
> - num_dimm);
> - } else {
> - pr_info("This system has a very crappy BIOS: It doesn't even list the DIMMS.\n");
> - pr_info("Its SMBIOS info is wrong. It is doubtful that the error report would\n");
> - pr_info("work on such system. Use this driver with caution\n");
> - }
> + if (!fake) {
> + pr_info("This EDAC driver relies on BIOS to enumerate memory and get error reports.\n");
> + pr_info("Unfortunately, not all BIOSes reflect the memory layout correctly.\n");
> + pr_info("So, the end result of using this driver varies from vendor to vendor.\n");
> + pr_info("If you find incorrect reports, please contact your hardware vendor\n");
> + pr_info("to correct its BIOS.\n");
> + pr_info("This system has %d DIMM sockets.\n", num_dimm);
> + } else {
> + pr_info("This system has a very crappy BIOS: It doesn't even list the DIMMS.\n");
> + pr_info("Its SMBIOS info is wrong. It is doubtful that the error report would\n");
> + pr_info("work on such system. Use this driver with caution\n");
> }
>
> if (!fake) {
> - /*
> - * Fill DIMM info from DMI for the memory controller #0
> - *
> - * Keep it in blank for the other memory controllers, as
> - * there's no reliable way to properly credit each DIMM to
> - * the memory controller, as different BIOSes fill the
> - * DMI bank location fields on different ways
> - */
> - if (!ghes_edac_mc_num) {
> - dimm_fill.count = 0;
> - dimm_fill.mci = mci;
> - dmi_walk(ghes_edac_dmidecode, &dimm_fill);
> - }
> + dimm_fill.count = 0;
> + dimm_fill.mci = mci;
> + dmi_walk(ghes_edac_dmidecode, &dimm_fill);
> } else {
> struct dimm_info *dimm = EDAC_DIMM_PTR(mci->layers, mci->dimms,
> mci->n_layers, 0, 0, 0);
> @@ -497,12 +489,8 @@ int ghes_edac_register(struct ghes *ghes, struct device *dev)
> if (rc < 0) {
> pr_info("Can't register at EDAC core\n");
> edac_mc_free(mci);
> - mutex_unlock(&ghes_edac_lock);
> return -ENODEV;
> }
> -
> - ghes_edac_mc_num++;
> - mutex_unlock(&ghes_edac_lock);
> return 0;
> }
> EXPORT_SYMBOL_GPL(ghes_edac_register);
> @@ -510,15 +498,9 @@ EXPORT_SYMBOL_GPL(ghes_edac_register);
> void ghes_edac_unregister(struct ghes *ghes)
> {
> struct mem_ctl_info *mci;
> - struct ghes_edac_pvt *pvt, *tmp;
> -
> - list_for_each_entry_safe(pvt, tmp, &ghes_reglist, list) {
> - if (ghes == pvt->ghes) {
> - mci = pvt->mci;
> - edac_mc_del_mc(mci->pdev);
> - edac_mc_free(mci);
> - list_del(&pvt->list);
> - }
> - }
> +
> + mci = ghes_pvt->mci;
> + edac_mc_del_mc(mci->pdev);
> + edac_mc_free(mci);
> }
> EXPORT_SYMBOL_GPL(ghes_edac_unregister);
>